The present invention relates to instruments and methods for treating atrial fibrillation, and more particularly to a surgical instrument and method for ablating cardiac tissue using radiofrequency energy.
Cardiac arrhythmias, such as atrial fibrillation, are a commonly occurring disorder characterized by erratic beating of the heart. The regular pumping function of the atria is replaced by a disorganized, ineffective quivering caused by chaotic conduction of electrical signals through the upper chambers of the heart. While medication can be an effective treatment for some cases, many patients are not responsive to medical therapies and require alternative treatment. As an alternative to medication, a surgical technique, known as the Maze technique, requires open chest surgery to strategically incise the atrial wall, and subsequently repair the incisions by suturing. The result of this surgery is to create scar tissue located along the incision lines and extending through the atrial wall to block electrical conductivity from one segment to another.
While the Maze procedure has proven effective in restoring normal sinus rhythm, it requires considerable prolongation of cardiopulmonary bypass and aortic crossclamp time, especially when performed in combination with other open heart procedures. Over the last decade, more simplified techniques have been proposed which replace surgical incisions with ablations, or scars, formed in the heart tissue. The various energy sources used in ablation technologies include cryogenic, radiofrequency (RF), laser, and microwave energy. The ablation devices are used to create tissue lesions in an affected portion of the heart in order to block electrical conduction.
One common ablation technique employs the use of a catheter that is introduced into the heart (e.g., intravascularly) to direct RF energy at specific areas of heart tissue found to be the source of the irregular rhythms. An electrophysiology (EP) study is first performed to discover the location and characteristics of the arrhythmia and, once the specific location is identified and mapped, RF energy is delivered to the tissue to ablate the tissue, thus forming a lesion that blocks electrical conduction. While minimally invasive techniques are usually preferred, the procedure is often performed in combination with other open heart procedures as a prophylactic to prevent post-operative onset of atrial fibrillation.
RF ablation techniques are typically successful in treating atrial fibrillation, however the A lesions must be well defined within the heart to be effective. The lesion must have a sufficient length, continuity and/or depth to interrupt or to block electrical conduction across the affected portion of the heart. This can be difficult to achieve without forming an incision in the atrium. In addition, if the energy is not uniformly transmitted to the target site, hot spots can form, possibly leading to severe tissue damage or blood coagulation (clots).
Accordingly, there exists a need for ablation instruments and procedures that produce uniform ablations on a retracted atria.
The present invention provides ablation systems and methods for treating atrial fibrillation utilizing RF energy. The ablation system generally includes two components: a first conductive component adapted to be placed on or adjacent to a first tissue surface, and a second conductive component adapted to be placed on or adjacent to a second, opposed tissue surface. Both components are effective to communicate with a source of ablative energy. The first component is shaped to conform to a desired lesion pattern, or portion of a lesion pattern. In use, ablative radiation is transmitted from the second component through the tissue to the first component to form the desired lesion pattern, or portion of a lesion pattern.
In one embodiment, the first component is an elongate conductive member and the second component is a tissue piercing element. The elongate conductive member is in communication with a source of ablative energy and is adapted to be positioned on a tissue surface. A plurality of openings, each having a specific diameter, are formed in the elongate conductive member. The openings can be spaced apart by a distance such that, together, the openings form a portion of a lesion pattern. The tissue piercing element, which is electrically isolated from the elongate conductive member, has a diameter less than the diameter of each opening in the conductive member, and is adapted to be deployed through each of the openings in the elongate conductive member. In use, the tissue piercing element is effective to transmit ablative energy through the tissue surface to the conductive member to form a lesion having a desired lesion pattern.
The tissue piercing element can include a proximal end and a distal end adapted to be selectively deployed into tissue through each of the plurality of openings. A first conductor element effective to communicate with a source of ablative energy can extend from the conductive member, and a second conductor element effective to communicate with a source of ablative energy can extend from the tissue piercing element. In a preferred embodiment, the tissue piercing element is an energy transmitting electrode and the elongate conductive member is a return electrode.
In another embodiment, an insulative coating is disposed around the circumference of each of the plurality of openings in the elongate conductive member, or alternatively such a coating is disposed around a portion of the tissue piercing element. The insulative coating is effective to electrically isolate the conductive member from the tissue piercing element.
In yet another embodiment, the elongate conductive member includes a top surface and a bottom, tissue contacting surface. The bottom surface can include an adhesive for selectively securing the elongate conductive member to tissue. The elongate conductive member can optionally be malleable to allow the conductive member to be formed into a desired shape to conform to the tissue on which it is placed, or to form a desired lesion pattern.
In other aspects according to the present invention, the tissue piercing element includes a flashback lumen extending between a fluid entry port formed on the distal end of the tissue piercing element and a fluid exit port formed on a proximal portion of the tissue piercing element. The flashback lumen is effective to indicate the position of the distal end of the tissue piercing element when inserted through one of the plurality of openings in the conductive member, thereby providing an indication of the penetration depth.
In another embodiment, the first component of the surgical ablation system is a return electrode and the second component is an energy transmitting electrode. The return electrode is movable between a first, retracted position and a second, open position wherein the return electrode assumes a substantially circumferential shape. The energy transmitting electrode is effective to transmit ablative radiation between intervening tissue and the return electrode member to form a substantially circumferential lesion pattern. The system can also include an introducer element having an inner lumen formed therein and being adapted to receive the return electrode in the retracted position.
Methods of ablating tissue are also provided. In one embodiment, a conductive member is provided having a plurality of openings and being effective to communicate with a source of ablative energy. A tissue piercing element electrically isolated from the conductive member and in communication with the source of ablative energy is also provided. The conductive member is positioned on a first surface of a target tissue, such as cardiac tissue. The tissue piercing element is then deployed through a first one of the plurality of openings to position a distal end of the tissue piercing element adjacent a second, opposed surface of the target tissue. Once the tissue piercing element is properly positioned, ablative energy is transmitted between the distal end of the tissue piercing element, intervening target tissue, and the conductive member to form a lesion segment in the target tissue. The steps of deploying the tissue piercing element and transmitting ablative energy are repeated at each of the plurality of openings to form a lesion of a desired size and pattern. Preferably, the openings are spaced apart at a distance such that the plurality of lesion segments overlap to form a single, elongate lesion.
In another embodiment, an introducer element is provided having an inner lumen formed therein. A return electrode is also provided and is effective to communicate with a source of ablative energy. The return electrode is movable between a first, retracted position wherein the return electrode is disposed within the inner lumen of the introducer element, and a second, open position wherein the return electrode has a substantially circumferential shape. The introducer element is inserted through a tissue surface with the return electrode in the first, retracted position. The return electrode is then moved to the second, open position. Ablative energy is then transmitted between the energy transmitting electrode, intervening target tissue, and the return electrode while the energy transmitting electrode is moved around the circumference of the return electrode, thereby forming a substantially circumferential lesion.